Catalyst for treating combustion exhaust gas

ABSTRACT

THE EXHAUST GAS DISCHARGED FROM INTERNAL COMBUSTION ENGINES OR THE LIKE IS TREATED TO CONVERT HARMFUL OR NOXIOUS POLLUTANT COMPONENTS SUCH AS NITROGEN OXIDES, CARBON MONOXIDE AND UNBURNED HYDROCARBONS TO INNOCOUS COMPOUNDS, BY CONTACTING THE EXHAUST GAS WITH TWO STAGES IN SERIES OF A CATALYST COMPOSITION CONTAINING 5.0 TO 12.0% BY WEIGHT OF COPPER AS A EQUIVALENT COPPER OXIDE AND 0.5 TO 4.0% BY WEIGHT OF COBALT AS EQUIVALENT COBALT OXIDE, DEPOSITED ON PARTICLES OF ALPHA ALUMINA. THE CATALYST MAY ALSO CONTAIN A SMALL PORPROTION OF MANGANESE. AIR IS INJECTED INTO THE PARTIALLY REACTED EXHAUST GAS BETWEEN STAGES, SO THAT A REDUCTION OF NITROGEN OXIDES TAKES PLACE IN THE FIRST CATALYTIC STAGE OR BED, AND OXIDATION OF CARBON MONOXIDE AND HYDROCARBONS TO INNOCUOUS COMPOUNDS SUCH AS CARBON DIOXIDE AND WATER VAPOR TAKES PLACE IN THE SECOND CATALYTIC STAGE OR BED.

United States Patent O NE brawing. Filed Sept. 13, 1971, Ser. No. 180,108 Int. Cl. B013 11/08, 11/32 U.S. (:1. 252-466 J 3 Claims ABSTRACT OF THE DISCLOSURE The exhaust gas discharged from internal combustion engines or the like is treated to convert harmful or noxious pollutant components such as nitrogen oxides, carbon monoxide and unburned hydrocarbons to innocuous compounds, by contacting the exhaust gas with two stages in series of a catalyst composition containing 5.0 to 12.0% by weight of copper as equivalent copper oxide and 0.5 to 4.0% by weight of cobalt as equivalent cobalt oxide, deposited on particles of alpha alumina. The catalyst may also contain a small proportion of manganese. Air is injected into the partially reacted exhaust gas between stages, so that a reduction of nitrogen oxides takes place in the first catalytic stage or bed, and oxidation of carbon monoxide and hydrocarbons to innocuous compounds such as carbon dioxide and water vapor takes place in the second catalytic stage or bed.

The present case is a division of US. patent application No. 55,998 filed July 17, 1970 and allowed on Dec. 30, 1971 and thereafter abandoned in favor of continuation US. patent application No. 237,516 filed Mar. 23, 1972.

BACKGROUND OF THE INVENTION Field of the invention Description of the prior art In recent years it has been recognized that the exhaust gas discharged from internal combustion engines is a serious source of air pollution, especially in metropolitan areas. In some cases, a so-called smog is generated due to atmospheric inversions and accumulation of such exhaust gases in the atmosphere. Recent attempts to prevent such air pollution have concentrated on the destruction or elimination of noxious components by catalysis, especially by admixture of secondary air into the exhaust gas followed by catalytic oxidation of residual hydrocarbons, carbon monoxide, etc., in various types of apparatus specially designed for this purpose. Improvements in active catalytic agents for this function are described in US. Pats. Nos. 3,053,773; 3,429,656; 3,316,057 and 3,476,508. Copper-bearing catalysts are generally described in US. Pats. Nos. 3,398,101; 3,477,893, 3,493,- 325 and 3,133,029. A typical two-stage apparatus for carrying out the process with interstage air injection is described in US. patent application No. 33,359 filed Apr. 30, 1970, now US. Pat. No. 3,656,915.

Summary of the invention In the present invention, it has been determined that a catalytic agent containing copper in the range of 5.0% to 12.0% by weight of equivalent copper oxide and cobalt in the range of 0.5% to 4.0% by weight of equivalent cobalt oxide deposited on alpha alumina particles provides a highly effective catalyst for treating exhaust gases from internal combustion engines or the like, in order to reduce nitrogen oxides to nitrogen, and also oxidize carbon monoxide and residual vaporous hydrocarbons to carbon dioxide and waste vapor. The catalyst may also contain 0.5% to 2% manganese dioxide. The copper will generally be present as CuO and the cobalt will generally be present as C0 0 however these metals may be at least partially present as reduced oxides or in the metallic state. Similar considerations apply to manganese, when present. In the description and claims infra, catalyst compositions will refer to these metallic components in terms of equivalent oxide content, however the copper and cobalt may be partially present in actuality as other compounds or as reduced elemental metals or in the metallic state. However, equivalent oxide composition in accordance with the formulas supra is reported on analysis, as is customary in the art.

The exhaust gas is passed through two catalyst beds or masses in series containing copper oxide and cobalt oxide deposited on particles of alpha alumina. Air is injected into the partially reacted gas between the beds or stages, so that the initial bed functions as a reducing medium to eliminate nitrogen oxides and the final bed acts as an oxidizing agent to oxidize carbon monoxide and residual hydrocarbon vapors. It has been determined that highly beneficial results are thereby attained, in terms of removal of nitrogen oxides from the exhaust gas by reduction, and removal of carbon monoxide and hydrocarbon vapors by oxidation, due to the synergistic action of the copper and cobalt together with the alpha alumina. Thus, the invention is practiced with two catalyst beds in series, in which series flow of exhaust gas takes place through the two beds and air which may be preheated is injected into the partially reacted exhaust gas between beds. A typical apparatus for carrying out the process is described in US. patent application No. 33,359 filed Apr. 30, 1970, now US. Pat. No. 3,656,915. A temperature level generally in the range of 200 C. to 800 C. will usually be provided in the catalyst beds during reaction, however the invention may be practiced at lower temperatures, such as when starting a cold automobile engine, or at temperatures above 800 C.

It is an object of the present invention to provide an improved process and catalyst for treating exhaust gases from internal combustion engines to remove noxious components.

Another object is to prevent air pollution due to the discharge of exhaust gas from internal combustion engines.

A further object is to provide an improved process and catalyst for catalytically reducing nitrogen oxides and oxidizing carbon monoxide and hydrocarbon vapor in the exhaust gas from an internal combustion engine.

An additional object is to provide a synergistic combination of specific proportions of copper and cobalt together with alpha alumina, in a catalyst composition for treating the exhaust gas from internal combustion engines.

These and other objects and advantages of the present invention will become evident from the description which follows.

3 DESCRIPTION OF THE PREFERRED EMBODIMENTS AND EXAMPLES A catalyst composition was prepared in accordance with the present invention. The catalyst was prepared by double impregnation of alpha alumina particles with the nitrate salts of the catalytically active metals: Copper (Cu) and Cobalt (Co). Some ammonium nitrate was also added to assist in the activation procedure. The nitrates are decomposed at 210 C. to 230 C. for a period of at least 24 hours, and preferably 48 hours. Activation is completed by reducing the catalyst at 400 C. to 450 C. with hydrogen. Catalyst compositions were prepared or formulated in a series of tests with equivalent copper oxide content varying from 5.0% to 12.0% by weight, and equivalent cobalt oxide content varying from 0.5% to 4.0% by weight, deposited on alpha alumina. Following are the test results.

Example I TABLE I.COMPOSITION RANGE OF CATALYST Percent CuO 6.90-1030 Percent C 0 0.78-1.54

TABLE II.TWO STAGE REACTOR TEST RESULTS* Component in gas Inlet gas Exit gas NOx (p.p.m.) 1,350 216 CO (percent) 2.84 0 OuH1 (p.p.m.) 1, 450 22 Temperature C 4 770 Oz in exit gas (percent) 1.0

* With interbed air injection.

TABLE III.STABILITY TEST Space velocity v./v./hr. 9600 Total reaction time (hours) 4 Temp. at start of test, C 700 Maximum temp. reached, C. 800 Temp. at end of test, C. 360 Inlet NOx content (p.p.m.) 1780 Exit NOX (700-800 C.) ppm. Exit NOx (350-360" C. p.p.m. 90 Crush strength at completion 90# TABLE IV.SUMMARY OF EXTENDED STABILITY TESTS Time of test (hours) 114 Space velocity (v./v./hr.) 12,700

Percent conversion of 0.24% NOx 1 96.2 Percent conversion of 0.24% NOx 2 97.6

1 (Average of 8 hr. tests at 200 C.). 2 (Average of 106 hr. tests at 450 0.).

Example II.Efiect of hexane TABLE V.--FEED GAS COMPOSITION Component: 4 Concentration 0 percent 4.6 CO do 1.6 NOx do 0.24

CGHM p.p-.m N Remainder TABLE VI.EXIT GAS COMPOSITION AT VARYING TEMPERATURE C 0 ant:

iyer c ent O: 3. 4 3. 6 2. 5 Percent (30..... 0.0 0. 0 0.0 0.24 0.24 0.24 90 44 8 2.4 2.4 2.0 Remainder Remainder Remainder Example III-Effect of infrared air injection TABLE VII.-GAS COMPOSITION Concentration Final gas Without air With air Feed gas, injection, injection, percent percent percent Component:

1 Parts per million.

Space velocity was 11,500 hrf except after air injection when S.V. was 13,000 hr.- Feed gas temp. was 250-300 0., exit first stage temp. was 480-495 C. and NOx was 107 ppm.

Example IV.Effect of manganese The manganese modification of the basic copper-cobalt catalyst was made by formulating a catalyst composition with the following analysis range.

TABLE VIII.MANGANESE MODIFICATION CATALYST ANALYSIS Percent CuO 9.5-115 Percent C0 0 2.5-3.5 Percent MnO 0.5-2.0

TABLE IX.- EST RESULTS USING TABLE VIII CATALYST Tests were made in a two-stage reactor with added air in the second stage. Gas temperature was 250 C. to 350 C. and space velocity was 11,000 to 16,000 v./v./hr. Following are the test results.

Exit gas at time of test Test gas 0900 hrs. 1100 hrs.

Component:

Percent 01. 0.0 1.0 1.0

Percent CO 1.98 0.0 0.0

Percent 002. 15.81 16. 8 17.0

Percent N2" 82. 21 82. 2 82.0

NOx (ppm. 2,280 355 320 CsHu (p.p.1n.) 1 1 Exit gas at time of test Test gas 1300 hrs. 1600 hrs.

Component:

Percent 02. 0. 0 0. 60 1. 6

Percent CO 1.19 0.0 0. 0

Percent 002 8. 69 9. 4 10. 0

Percent Nr 90.12 89.9 88. 4

NO): (p.p.m.) 1, 420 105 230 051114 (p.p.m.) 200 2 1 Following are the test results for a single stage reactor using the manganese-modified catalyst.

Exit gas Test gas Run #1 Run #2 Component:

Percent 02 0.60 0. 20 0. 20

Percent 00. 2.19 0. 00 0. 00

Percent 001. 14. 42 16.42 16.06

Percent N2 s2. 79 83.38 83. 74

NOx (p.p.m. 1, 000 10 10 CaHu (propylene) 425 4 4 All of the gas analyses supra in Example are on a dry gas basis, however the tests were run with 10% to 13% water vapor in the feed gas.

We claim:

1. A catalyst composition for the treatment of exhaust gas from an internal combustion engine to remove noxious Wm and second stages of twoastage reactor.

components which comprises between about 5.0% to 12.0% by weight of copper as equivalent copper oxide, between about 0.5% to 2.0% by weight of manganese as equivalent manganese dioxide, and between about 0.5% to 4.0% by weight of cobalt as equivalent cobalt oxide, deposited on alpha alumina.

2. The composition of claim 1, in which said copper and cobalt are at least partially present in said catalyst composition in the form of reduced oxides.

6. The composition of claim 1, in which said catalyst composition contains between about 9.5% to 11.5% by weight of copper as equivalent copper oxide and between about 2.5% to 3.5% by weight of cobalt as equivalent cobalt oxide.

References Cited UNITED STATES PATENTS 3,447,893 6/1969 Stephens et al. 252-474 X 3,295,918 l/1967 Briggs et a1. 252471 X CARL F. DEES, Primary Examiner US. Cl. X.R. 

